It is conventional to form a plurality of power transmitting belts from a vulcanized sleeve. Such sleeves are conventionally formed by wrapping successive layers of the belt components about a mandrel. Upon completion of the vulcanization of the sleeve, the sleeve is cut lengthwise to define a plurality of separate belt preforms.
It is conventional to cut the belt elements to the desired trapezoidal shape so as to define individual V-belts without further machining operations. A problem has arisen, however, in connection with such belt manufacture, in that the V-belts often vary from one to the other in length and cross-sectional shape due to machining errors such as may result, for example, from the thermally shrinking material characteristics of the belt. Further, the tensile elements of the belt are often displaced causing shortened useful life of the belt in power transmission use.
Alternatively, the sleeve may be cut to the desired shape before vulcanization and the individual belts vulcanized in a suitable mold. Such manufacture similarly does not provide completely satisfactory belt structures.
It is common to form the side surfaces of the belt by grinding. Such grinding of the belt material, however, may not only affect the length of the belt but vary the position of the belt relative to the axial center of the pulleys with the belt entrained thereabout.
As a result of the inaccuracies in such manufacture, conventional power transmission belts are often subject to vibration and variation in belt tension during use not only causing shortening of the useful life of the belt but producing undesirable vibrations in the machine being driven.
Because of the variations in the belt dimension, it has been common to measure the respective belts to select those having the proper dimensional characteristics and subjecting those that do not have the desired characteristics to further forming steps such as grinding of the side surfaces of the belt so as to permit the belt to seat more deeply in the pulley and thereby shorten the effective length of the belt.
It is known to effect the separation of the vulcanized sleeve into individual V-belts by the use of a rotating grinder rather than cutting tools. Further, the V-shaped portion of the belt may be formed by an abrasive plate while rotating the sleeve on a mandrel with the individual V-belts then being separated from each other by a suitable cutter.
The use of grinding or abrasive means in forming the V-shaped belt has the disadvantage of causing the surface temperature of the rubber to be relatively high such as 100.degree. C. or higher as a result of the frictional heat developed in the grinding operation. Such high temperature causes the molecular bonds of the surface rubber to be broken and thereby causes the surface rubber to be devulcanized. The pressure and frictional forces required in such grinding operations may distort the rubber so that the grinding operations may not result in an accurately preselected V-shaped configuration of the belt.
A further problem arises in such grinding of the belt in that variations in the hardness of the rubber require different abrasive characteristics and thus the grinding means is not always accurately coordinated with the requirements of the material being ground, resulting in defective belt manufacture.
The forming of the V-belts by such grinding manufacture has the further disadvantage of necessitating the use of a substantial number of manufacturing steps and handling operations increasing the costs and manufacturing time.